Tag Archives: lens

January 27, 2008 · 8:28 pm

Shooting Through a Fence

In the last lesson, I talked about shooting at the zoo under difficult circumstances and how to break the problem down into manageable pieces. One of the problems that TJ faced was that there was a fence between him and the subject. I promised to take a few sample shots through a fence and show what effects different apertures had on the image.

The following images were all shot with a Canon Digital Rebel XT and the Canon 50mm f/1.8 lens, also known as the nifty fifty. I chose it because I wanted to be able to open up the aperture in order to blur the fence as much as possible. Here are three sets of images that show how the fence looks from different distances at different apertures. I apologize for not finding more interesting subjects, but these were taken during a quick stop at the Port of Oakland when I was late for work.

In the first set, the camera is just a couple of inches from the fence. The camera was in aperture priority mode, and the four shots were taken at f/2, f/4, f/8, and f/16. As you can see, at f/2, the fence blurs so much that it’s essentially invisible. At f/4, you can start to see the fence blurring parts of the image. At f/8 the fence is quite visible, and at f/16 it’s almost sharp.

This time, I’m standing about an arms length away from the fence. At f/2, the fence is just a blurry grid. At f/4 it starts to look like a fence, at f/8 it’s clearly a fence, and at f/16 it’s fairly sharp.

In the final set I’m standing about five feet away from the fence, and also at a slight angle. At f/2 the fence is a blurry mess, at f/4 it starts to sharpen up, and at f/8 and f/16 it’s sharp enough to work as part of the image rather than being a flaw.

Conclusion: if there’s a fence in your way, figure out what you want to do about it and adjust accordingly. If you want to make the fence disappear, get as close to it as you can, and open up your aperture as wide as possible. If you want to use the fence as part of the image, back up a bit and stop down.

3 Comments

Filed under Discussion, Lesson, Question

Tagged as canera, lens, photography

January 23, 2008 · 10:55 pm

Question: Shooting At The Zoo

I recently got an excellent reader question from TJ. It was such a great question that I thought it deserved its own entry, rather than being buried in comments.

Patti, I had a really frustrating experience last year when I attempted to take pictures at a zoo. Most of the occupants were birds and were housed behind 1″ grid wire. Frequently, they were shaded and I (and the camera) were not. Sometimes they were moving. Sometimes I had to shoot up into a tree and the sun was shining directly into the lens. Often, my camera wouldn’t focus, so I had to shift to manual focus. Sometimes, it wouldn’t even snap the picture when I was doing the focusing. I have a Nikon D70s. Might you give some tips on what I could’ve been doing wrong and how to shoot these types of pictures better?

TJ, that’s a really hard set of circumstances to work under, because you have so many things working against you. This is exactly the sort of situation that will confuse automatic modes on your camera, and require you to switch to manual settings in order to get good shots. I’m not sure I have a magic formula, but let me see if I can break the problem down and show you how I’d think about it.

First the fence. It’s going to do two things– get in the way of your shooting, and confuse your autofocus. Switching to manual focus is a great way to solve the latter problem, since you’re smarter than the camera is and you know to just ignore the fence. Once you’re in manual focus, you have two choices on how to deal with the fence– you can either stand back and use the fence as part of the composition, or you can put the lens up against the fence and shoot between the grids. Using a wide aperture will help the fence blur and fade out of the picture, especially if you’re close to it.

Here’s where things are going to get hairy and conflict with each other. You’re manually focusing on a moving target, so you sort of want to leave yourself some room for error– if you have a lot of depth-of-field, you’ll still have the bird in focus even if he starts moving. However, that’s in direct conflict with wanting to use a wider aperture to make the fence fade away. I would probably opt for using something like f/5.6 (I originally said f/11, but in retrospect I think that’s probably not the best answer) and then get as close to the fence as I could, but I’d play around with it and see what worked for that particular situation.

Once I found an aperture that I liked, I’d try to find the best shutter speed that worked with it. If I couldn’t get a fast enough shutter speed to capture the birds well, I’d increase the ISO until I did. If that still didn’t work, I’d open up the aperture until I found something that worked. There’s a pretty good chance that the camera’s metering will be confused here, so use it as a starting point rather than a final answer.

This is one of those places where digital has a huge advantage over film– you can try out the shot and see how it works. The birds aren’t going anywhere, so you can afford to spend a few minutes setting up a few shots and seeing what works, then making adjustments. Whenever I’m shooting under tricky lighting conditions, I always do a few test shots beforehand so that I can get my camera set up the way I want it.

Backlighting, especially shooting into the sun, is just hard. Don’t forget that your feet are an invaluable photographic tool. If you can’t get the shot because the sun is right in front of you, take a few steps. You’ll probably be able to find a better angle on your subject. If you’re close enough that you can use a flash to fill in some front light, that often works very well.

I haven’t used a Nikon dSLR, so I don’t know what will stop it from taking a shot. I know that my Canon will stomp its foot and get pouty if it can’t focus, but if I put it into manual focus it will shoot with the lens cap on in all exposure modes.

After I answered this question, I went out and took a few photos through a fence, to see what the fence looked like at different apertures and distances. I’ll post them as a separate entry.

By the way, the bird photo at the top of this entry was taken at the St. Louis Zoo a few years ago, shortly after I got my first dSLR. I can’t remember much about the photo, but it was taken through either glass or a fence in auto mode. I included it partially because it matched the subject matter, but mostly to remind myself that just a little while ago all I really knew how to do was point the camera at something and hope for the best.

What do lens terms mean?

If you’ve just gotten your first dSLR, you’ve probably already thought about buying another lens to go with it. Maybe you want something that will let you shoot telephoto, or wide angle, or macro. Maybe you want something faster. Most likely, you don’t know what you want, but somebody told you that the kit lens wasn’t very good and you believed them.

You did what anyone would do, and started surfing the web looking at lenses. Pretty soon, your head was swimming and your eyes were glazed over after looking at all those lens terms. What’s an EF-S? What does 70-200 mean? Why is that lens so much more expensive than the one that seems like the same thing?

I’ll do my best to unravel it all for you, though I’ll warn you up front that some of this is Canon-specific. If anyone wants to write a guest entry and explain Nikon-specific terminology, or terminology for other brands, leave me a comment.

First off, an easy one. The writing on the front reads “CANON LENS EF 50mm 1:1.8 II CANON INC. (theta)52mm”. This is the Canon “Nifty Fifty” 50mm lens. (It’s a steal at around $75, and I highly recommend picking one up if you shoot Canon.) The “CANON LENS” is easy enough that I won’t insult your intelligence by explaining it.

“EF” is a Canon-specific term, and it stands for Electro-Focus. This is the type of lens that is used on the Canon EOS line of SLRs. As of this writing, all digital SLRs are EOS-type cameras, so if you have a Canon dSLR any EF lens should work. Some lenses are EF-S rather than EF. The S stands for “sticks out in back” or something like that– the back part of the lens sticks out a little farther than an EF lens. If you have the Canon 18-55 kit lens, it’s an EF-S mount. EF-S lenses work on almost all Canon dSLRs except for the high-end professional models.

“50mm” is the focal length of the lens– I explained what focal length is in the previous entry. 50mm is kind of a mid-range focal length, neither long enough to be telephoto nor short enough to be wide-angle. It’s a good general-purpose length.

“1:1.8” is the maximum aperture of the lens– the widest that it can open. The term “1:1.8” means exactly the same thing as f/1.8, and we all know what f-stops are now, right? Right?

I’ll be perfectly honest here and say that I’m not certain what the “II” means, but I’m guessing it means something like “Version 2”.

On the other side of the lens it says “CANON INC.” and then “52mm”. That last number is the size of the filter threads. Almost all lenses have threads on the outside that will let you screw a filter onto the front, either to protect the front glass from damage or to add some sort of special effect. On this particular lens, the diameter of the threads is 52mm, which means that you need to buy a 52mm filter if you want to add a filter. It is common practice and a very good idea to keep a UV filter on the front of your lens at all time, to protect the lens from damage.

Here’s the Canon kit lens. It’s a lot like the previous one, but a little bit more complicated.

Notice that instead of “CANON LENS” it says “CANON ZOOM LENS”. The word zoom means that the lens can change its focal length. In the previous example, the 50mm lens was always 50mm and you couldn’t make the focal length any longer or shorter. In the case of a zoom lens, there’s an extra ring on the lens that lets you zoom in or out to get closer or farther away from your subject. In this case, if we look just a little bit farther on the lens, we’ll see “18-55mm”. That means that the lens can zoom out to be as wide as 18mm, or zoom in to get as close as 55mm. You can, of course, use any length in-between those as well. Zoom lenses are nice because they let you have a lot of flexibility in how the image looks without having to change to a different lens.

I’ve already explained the “EF-S” part, but I’ll remind you that it’s Canon-specific.

Now it gets interesting. The maximum aperture is listed as “1:3.5-1.5.6”. We already know that means f/3.5-f/5.6, but why would a lens have more than one number? As it turns out, zoom lenses are really nice to use, but they’re harder to make than fixed-focal-length (also called “prime”) lenses. Some zoom lenses have the same maximum aperture at both their shortest and longest focal lengths, but sometimes the maximum aperture changes. When you see two numbers, the first one is what the maximum aperture is when the lens is at its shortest focal length, and the second one is at its longest.

In this case, that means that when the lens is zoomed out to 18mm, the widest possible aperture is f/3.5. When it’s zoomed in to 55mm, the widest it can open is f/5.6. As you can probably guess, if you’re in the middle of that range the maximum aperture is somewhere between those two values.

Finally, this lens has 58mm filter threads.

There are a few more terms you’ll commonly see for Canon lenses. “USM” stands for ultrasonic motor, and specifically the motor that is used for focusing. All you really need to know is that USM lenses focus faster than their non-USM counterparts, and they’re quieter.

“IS” stands for image stabilization. This is a piece of real technical magic that helps get rid of camera shake on longer exposures. It can be extremely useful for getting shots where you can’t quite hold the camera steady enough to get a solid shot. It won’t help you with moving subjects, and it won’t do any good for very long exposures, but it’s great when there’s almost but not quite enough light. IS lenses are much more expensive than their non-IS counterparts, though.

And finally, some Canon lenses have the “L” designation. This stands for “Ludicrously Expensive.” OK, not really, but it might as well. Canon L lenses are their top-of-the-line professional models. They are generally the highest-quality lenses that Canon makes, but they come with a high price tag.

I hope that helps, at least a little. Again, if someone wants to guest author a similar article about Nikon or other brand lenses, leave me a comment.

13 Comments

Filed under Equipment

Tagged as camera, lens, photography

January 11, 2008 · 12:23 am

What is focal length?

It happens to most dSLR owners. You get the camera, and you’re thrilled with it, but you’re also awed and a wee bit afraid because the whole thing is just so confusing. It doesn’t take very long before someone tells you that the kit lens, the lens that usually comes with the camera, is a piece of garbage. This sends you off to the web to find a better lens, but there are all sorts of complicated and cryptic numbers and letters and symbols and the like. The whole thing is so bewildering that you just want to go to the drugstore and buy a disposable film camera.

Don’t fear! The cryptic numbers and letters that are used to describe lenses are really (mostly) pretty straightforward. If you’ve been reading this blog, you’ll probably find that you’re already familiar with most of the terms, so this won’t be too hard.

Before we start looking at lenses, there’s on term that I may not have explained yet– focal length. In a nutshell focal length is how long the lens is. It’s a little bit more complicated than that, of course, and the technical definition isn’t all that interesting, but there is really only one thing you need to know, and it’s really easy. The longer your lens is, the more the image is magnified.

Let’s say that you’re taking a picture of the tree in your yard, and there’s a bird perched on a branch. If you use a short lens, you’ll get the whole tree into the picture, and the bird will be a tiny little blob. If you use a long lens, you’ll just get the bird and the branch that he’s sitting on, and you’ll be able to tell that he’s a blue jay. If you have a really long lens, you’ll be able to see the worm in his mouth. Cool!

If you have a zoom lens, and you probably do, you’re probably already familiar with this concept. Zoom in and everything gets closer. Zoom out and you get more of the area in the picture.

Long lenses are called telephoto lenses. The prefix tele- means distant, so telephoto lenses let you take pictures of distant things. This amazing shot of a polar bear, taken by award-winning nature photographer Joe Decker, was taken with a telephoto lens. Joe’s a smart guy, and he knows if he gets too close to a bear he runs the risk of being dinner.

Short lenses are called wide-angle lenses, because they let you get a really wide view of your surroundings. Again, I’ll use one of Joe’s photos, this one a sweeping view of sunrise in Bryce Canyon. I honestly don’t know what lens was used for this shot, but the only way to get such a grand vista is to use a wide-angle lens.

Here’s what you should remember about focal length: using a wide-angle lens is like stepping back from the picture so that you can see more of the action, while using a telephoto lens is like walking over to the subject so you can get a closer look. That’s really all you need to know for now.

Once again, I’d like to thank Joe Decker for giving me permission to use his images as examples. I highly recommend checking out his work, especially some of his recent images from Iceland and Greenland.

In the next lesson, I’ll take a closer look at a couple of lenses and explain what all of the numbers mean.

How the settings play together

After trudging through all those scary numbers, we now know that ISO 200 is twice as fast as ISO 100, that 1/60 second is half the time of 1/30 second, and that f/4 is twice as fast as f/5.6. If I did my job well, we even learned that without anyone’s brain dripping out of their ears and onto their keyboards.

Note: the word “fast” in photography generally means “captures more light” when it’s talking about ISO or aperture. When talking about shutter speed, though, “faster” means just the opposite– 1/60 is faster than 1/30, but 1/30 lets in twice as much light. It’s confusing.

What might or might not be obvious now is that we can change two different things and keep the exact same exposure. For example, each of these settings will produce the exact same exposure:

ISO 100	f/4	1/60 sec	baseline
ISO 100	f/2.8	1/120 sec	faster (wider, more light) aperture, faster (less light) shutter speed
ISO 200	f/4	1/120 sec	faster ISO, faster (less light) shutter speed
ISO 200	f/5.6	1/60 sec	faster ISO, faster (wider, more light) aperture
ISO 400	f/5.6	1/120 sec	ISO four times as fast, shutter speed twice as fast (less light), aperture half as fast (narrower, less light)

The first line is our baseline measurement. On the second one, we opened up the aperture wider to let more light in. In order to keep the exposure constant, we need to capture less of the light, so we keep the shutter open for half as long.

On the third and fourth lines, we increase the ISO, which records more light To balance it out, we either keep the shutter open for less time, or we make the aperture smaller– either of those will let less light in.

The fifth line is tricky! We’ve quadrupled the ISO, which means we’ve increased it by two stops. In order to compensate for that, we made the aperture smaller by one stop and we also made the shutter speed faster by one stop.

The fancy technical term for this is reciprocity– it really just means that if you change one setting, you can balance it out by changing another one, and get the same result.

So how would you use this? Here’s an example. Let’s say you’re taking a picture of a group of people, some of them standing behind the others. You put the camera in aperture priority mode and pick f/4 and ISO 100. When you try to take the shot, you find out that the best shutter speed is 1/30, and that’s too slow for you to hold the camera steady– you need at least 1/50 sec. What do you do?

Well, you can try using f/2.8 and 1/60. That will get you the same exposure, but at a faster shutter speed. But wait… now you’re at f/2.8, and when you focus on the front row of people the back row is out of focus, or vice versa. You really need f/4 to get everyone in focus.

Finally, you set the ISO to 200, which lets you use an aperture of f/4 with a shutter speed of 1/60. Voila! You get your shot.

The way exposure settings play together is a little bit like having a squishy ball in your hand. When you squeeze one part to make it smaller, another part gets bigger. Squish two parts, and the third one gets a lot bigger. Squish squish squish.

Easy, huh?

22 Comments

Filed under Aperture, ISO, Lesson, shutter speed

Tagged as camera, lens, photography

October 19, 2007 · 11:58 pm

How much more light? How much less?

At this point, we know what’s bigger and smaller, faster and slower. We know that f/4 is a bigger opening than f/8, and therefore lets more light in. We know that a shutter speed of 1/200 is faster than 1/100, and therefore lets less light in. We know that ISO 400 is faster than ISO 200, and therefore captures more light.

You’re with me, right? Good.

I’m about to throw a little bit of math at you, but I promise it’s only a tiny amount. No, really. All we really have to do is multiply by 2 or divide by 2. That’s easy, right? Take a deep breath. Ready? Let’s go.

How much more light does a shutter speed of 1/100 let in compared to a shutter speed of 1/200? The obvious guess is twice as much, and it’s precisely right. Any shutter speed that’s half as fast will let in twice as much light. Any shutter speed that’s twice as fast will let in half as much light. So 1/200 is half as much light as 1/100. 1/400 is half as much light as 1/200, and is therefore 1/4 as much light as 1/100. Double the bottom number means half as much light. Easy, huh?

Let’s look at ISO next. Do you think that ISO 200 is twice as much light as ISO 100? Bingo! Just like shutter speed, changing the setting by 2 means twice as much light, or half as much light. ISO 200 is half as fast as ISO 400. ISO 100 is half as fast as ISO 200, so it’s 1/4 as fast as ISO 400. Again, all you have to do is multiply or divide by 2, and you’re good.

Now aperture. Do you think f/4 is twice as fast as f/8?

Sorry, but this time it’s a tiny bit more complicated. When it comes to aperture, making the opening half as big means you’re only going to get 1/4 as much light. Making it twice as big means four times as much light. If you don’t want to know why, skip the rest of this paragraph. Our aperture is basically a circular opening. Remember back in high school, the area of a circle is pi-r-squared? Changing from f/4 to f/8 means that the radius of the opening is divided by 2. Because the area is changed by the square of the radius, the area of the opening is divided by 4. The amount of light coming in is directly related to the area of the opening, so the amount of light coming in is also divided by 4.

As it turns out, the way to cut the light in half is to change the aperture by a factor of about 1.4. In this case, f/5.6 is half as much light as f/4, and f/8 is half as much light as f/5.6.

Let me put it all into a nice tidy table, in case that’s easier to follow:

setting	Starting setting	1/2 as much light	1/4 as much light
ISO	400	200	100
Shutter Speed	1/100	1/200	1/400
Aperture	f/4	f/5.6	f/8

Now, a tiny bit of jargon. Whenever you increase or decrease the amount of light by a factor of 2, that’s called a stop. A shutter speed of 1/400 is one stop faster than 1/200. An aperture of f/4 is one stop wider than f/5.6. ISO 100 is one stop slower than ISO 200.

In summary: for shutter speed and ISO, changing the number by a factor of 2 means twice as fast or twice as slow. For aperture, changing the number by a factor of 2 means four times as fast or four times as slow. Half as much/twice as much is really all of the math you need to know in order to be a competent photographer.

A bonus note for those of you who are vaguely mathematically inclined. Remember that I said that changing the aperture setting by a factor of 1.4 meant twice as much or half as much light? The astute reader will note that 1.4 is (approximately) the square root of 2. That’s not a coincidence.

Next lesson: How the settings play together

13 Comments

Filed under Aperture, ISO, Lesson, shutter speed

Tagged as camera, lens, photography

October 15, 2007 · 11:46 pm

ISO: Why You Care

In the last lesson, you learned that ISO was sort of like turning up the volume on your stereo, in that it magnified the light as it came into your camera. That sounds like a pretty good way to get a brighter picture in low light, right? It is, but unfortunately there’s a cost associated with it.

Here are two utterly unremarkable photos that I took of the corner of my office building:

The first one was taken at ISO 100, the lowest my Canon Digital Rebel XT will go, and the second one was taken at ISO 1600, which is coincidentally the highest ISO that camera can do. You probably don’t see much difference in them at this size, but I promise you that they’re very different images.

Let’s go back to music for a bit. If you have a very quiet recording on your stereo and you turn it up, the sound gets louder. Something else happens, too– any background noises in the recording get magnified. If you’re listening to a tape (remember those?) the hiss of the tape gets louder. If there’s a small bit of noise in the background, it gets louder.

Just like sound recordings, our digital images exhibit something called noise, and that noise makes the images look grittier and grainier at high ISOs. For the following images, I’ve magnified everything to 2x the original size, and cropped down to a small section of the image for illustration purposes. First, let’s look at the upper left corner of the sky at ISO 100, 400, and 1600:

As you can see, the sky in the ISO 100 image is very smooth. At ISO 400 you can start to see it getting gritty, and at ISO 1600 the image looks pretty bad. That’s noise.

Here are a few more examples, at ISO 100 and ISO 1600:

In all three cases, the ISO 100 image looks pretty smooth, while the ISO 1600 image is very grainy.

It’s important to know that different cameras can have very different performance characteristics at higher ISOs. Inexpensive point & shoot cameras tend toward really horrible noise as the ISO increases, though I’m sure there are exceptions. Consumer-grade Canon digital SLRs are known for performing reasonably well at high ISOs, and their higher-end cameras often do exceptionally well. I have gotten some excellent low-noise shots out of my 5D at ISO 1600. Of course, I didn’t use that camera to take these test images, since the difference in quality would have been much more difficult to show.

If you’d like to see the full resolution versions of the originals:

ISO 100
ISO 400
ISO 1600

That’s great, but how should use use the ISO setting on your camera? My strategy is very simple. For typical shooting I always leave my camera set on ISO 100 until I find myself unable to get the aperture and shutter speed I need to get the shot. If there’s not enough light to shoot at ISO 100, I turn the ISO up until I get to an acceptable shutter speed and aperture. If I know I’m going to be shooting in a relatively dark environment like a nightclub, I just set the ISO to the highest setting I can and cope with whatever noise I get, since I already know that lower ISOs probably won’t be useful.

It can be useful to consider what you want to do with the images you shoot. If you’re just going to use them on the web, then the extra noise at higher ISOs won’t be much of a consideration, since the noise won’t be all that visible. Likewise, if you’re printing small images, noise won’t affect the output too much. However, if you’re planning to print enlargements, or you crop the image down significantly before printing it or displaying it on the web, noise may be a factor.

I hope that ISO has been demystified for you. Has it?

A quick update from mid-2010: This article was written a couple of years ago. Since then, dSLR technology has improved considerably. Many newer dSLRs can shoot very good images at ISO 800 or even 1600, and some produce usable shots at 3200 or even higher. All of the concepts remain the same, but the top end has moved a bit. I expect that will keep happening in the future.

Next lesson: How much more light? How much less?

3 Comments

Filed under ISO, Lesson

Tagged as camera, lens, photography

October 8, 2007 · 11:25 pm

ISO: What is it?

We’ve learned that the three things that control the exposure of a digital photo are shutter speed, aperture, and ISO. We know that shutter speed is how long the shutter is open, and that the longer it’s open the more light gets in. We know that aperture is how wide the lens is open, that wider openings let more light in, and that the size of the opening also controls how much of the image is in focus.

So what’s this ISO stuff? Way back when, we learned that there are magic gnomes that live on your camera’s sensor, and that when the shutter opens they record whatever light they see.

But first, a diversion. Imagine you go to a club to see a show– it’s a weird kind of show, but bear with me. There’s someone playing ballads on the guitar and singing along. There’s a guy playing punk rock on the accordion. There’s a trio singing political songs. And then someone gets up and whispers poetry. (Hey, I live in San Francisco. This kind of thing actually happens.)

All of a sudden, you can’t hear the show. The poem whisperer is much quieter than everybody who came before him, and the microphone isn’t sensitive enough to pick up his voice. Eventually someone kicks the sound guy and wakes him up, he turns up the sensitivity on the microphone, and unfortunately you get to hear the end of Ode to a Medium Rare Hamburger With Onions. Oh well.

Now our accordion player comes back for his Sex Pistols encore, and he blasts your eardrums. Whoops! Cover your ears until the sound guy turns the microphone’s sensitivity back down.

If you’d brought your camera you might have gotten a great picture of a room full of people covering their ears while staring at an accordionist, but other than that what does this have to do with photography?

Let’s go back to our imaginary gnomes who sit on your camera’s sensor waiting for light, and then record what they see. They do a great job on a bright sunny day, but what happens when you shoot inside the dark club? All of a sudden there’s not enough light for the gnomes, and you get a very dark image. You can open the aperture, but it only goes so far. You can use a slower shutter speed, but at some point you just get a blur of motion. There’s hope, though. Just like you have to turn up the sensitivity on the microphone to pick up more of a quiet sound, you can turn up the sensitivity on your sensor to pick up more light when the scene is dark. It’s like magnifying the light so that the gnomes can see it better.

That sensitivity is called ISO. Of course, there’s a technical description with lots of math stuff for exactly what it is and how it works, but the truth is that you don’t care. It doesn’t matter. Here’s what you do need to know about ISO– it’s pretty simple:

ISO 100 is generally considered the baseline, and it’s where your camera is set by default. ISO 200 is twice as sensitive as ISO 100. ISO 400 is twice as sensitive as ISO 200, and therefore four times as sensitive as ISO 100. ISO 800 is twice as sensitive as ISO 400, and ISO 1600 is… well, I’m not telling you. You’re smart enough to figure that one out on your own.

In the olden days, you bought film with a particular ISO, and you set your up camera so that it knew what film it had in it. These days, you just tell your camera what ISO that you want it to use, and it factors the ISO into its metering. Most dSLRs have a range of ISO from 100 to 1600, often 100, 200, 400, 800, and 1600. A few will have settings in between. Some will go as low as 50 and as high as 3200, and at least one model will go as high as ISO 6400. I’m pretty sure ISO 6400 will let you take pictures without taking the lens cap off.

See? That wasn’t so hard. Turning up the ISO is basically just magnifying the light that comes into your camera.

Next up: how to use ISO, and what side effects it has.

Next lesson: ISO: Why You Care

5 Comments

Filed under ISO, Lesson

Tagged as camera, lens, photography

October 6, 2007 · 11:49 pm

Exercise: Depth of Field

(This shall forever be known as the too-many-yellow-rulers lesson. Sorry!)

Up ’til now, you’ve been just reading the exercises and maybe doing them in your head, but not getting the camera out and trying them yourself. It’s OK– I’m lazy too. This one is different though. You’ll want to get the camera and do the exercise. If you don’t, I’ll hunt you down and scowl at you.

In this exercise, you’ll get firsthand experience with how aperture affects depth of field. In order to do the exercise, you’ll need a large flat surface with some sort of measurements, or sharp regular pattern. Some things that would work well:

a tile floor with high-contrast lines
a striped or checkered blanket with high-contrast lines
a long tape measure

You’ll need about five feet of this patterned surface, and you’ll need to be able to get fairly close to it, so that you’re looking down the length of it. See the tape measure picture at the top for an example of what I mean. You’ll also need enough light to take a steady picture at f/16.

Set your camera to aperture priority mode, f/16, and manual focus. If you’re not in a very bright area, set your ISO to 1600, or as high as your camera will go.

Stand near your patterned surface so that you’re looking down the length of it. Pick a spot in the middle, and manually focus on it. Remember that spot, because you’ll be coming back to it. Once you have the image in focus, take a picture.

Without changing your position, change the aperture to f/8. Point your camera at the exact same spot, and take another picture. Do the same thing at f/4, and as wide as your lens will go.

Pull the photos into your computer where you can examine them more closely, and you should have a set that looks something like the photos above. The photo taken at f/4 will have a narrow band in the center that’s in focus, and the rest will be blurry. The f/8 photo will have a wider focus area, and f/16 will be much wider.

For extra credit: repeat the exercise, but this time don’t take pictures. Instead, use the depth-of-field preview button on your camera to see what the shots would look like. Feel free to try out the apertures in between the ones I suggested too. You should see a much smoother transition of focus than at the widely-spaced apertures, of course.

The astute… OK, the barely-conscious reader will notice that the example photos in this exercise are also in the page header. I originally shot these as examples when I was teaching SSA! as a live class, and I wanted samples to hand out. I was happy when I saw the results. The students in the class seemed to grok depth of field as soon as they saw the images, and they had a field day duplicating them with their own cameras.

Now it’s time for you to go out and play. Put your camera in aperture priority mode, and wander around taking pictures. Create some blurry backgrounds and some crisp ones, just like you’ve always done, but this time do it on purpose. You have the power– use it.

Next lesson: ISO: What is it?

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Filed under Aperture, Exercise

Tagged as camera, depth of field, lens, photography

September 26, 2007 · 8:39 am

Depth of Field: Another View

We already know that depth of field is how much of your picture is in focus. In particular, it’s what distances from your lens are in focus. Is it a narrow range? A wide one?

Here are a few sample images that show you how depth of field actually works. I took these very carefully– I placed the camera on a tripod, and focused at exactly the 12-inch mark on the ruler. I made sure to keep everything lined up as carefully as possible, and then took shots at f/4, f/8, f/16, and f/32. Most lenses don’t go down to f/32, but this one did so it was good for shooting these sample photos:

At f/4, pretty much the only thing that’s in focus is the 12-inch mark itself– you can’t even read any of the other numbers. At f/8, you can start to see the numbers 11 and 13 come into focus, though they’re still a little soft. At f/16 the numbers 10-14 are pretty clear, and you can actually make out other numbers. At f/32 you can read the entire visible length of the tape measure, and the majority of it is fairly sharp.

I recommend clicking through on the above images and studying the larger images, since they give you a pretty good idea of how the depth of field breaks down as a percentage of the image. If you have a Flickr account, you can click the “all sizes” link above the photos to see them in their original eight-megapixel glory.

The astute reader will notice that these are the same images that are at the top of every page on this blog. I originally took them to use as examples when I was teaching Stop Shooting Auto! as a class for my coworkers, and I instantly loved them. They seemed to produce an aha! moment for everyone who saw them.

Let’s go back to our six-year-old’s landcscape for a bit. I’ve added something to the illustration this time– an indicator of what percentage of the image would probably be in focus at various apertures. The places where there’s a straight yellow line are the areas that will probably be in focus, and the angled lines indicate what will be out of focus– it’ll be just a little bit soft close to the solid yellow line, and stuff far away will be very blurry. Note that I guessed at these based on my experience rather than using any super-magical scientific math wizardry to figure it out. Treat them as rough guidelines rather than hard scientific fact.

Here’s how it might look at f/4:

and at f/8:

and finally, at f/16:

Clearly, if we want our image to be in focus across pretty much the whole range, we should use f/16 or smaller. If we want to blur most of the image, we should use a large aperture like f/4.

Tag Archives: lens

Shooting Through a Fence

Question: Shooting At The Zoo

What do lens terms mean?

What is focal length?

How the settings play together

How much more light? How much less?

ISO: Why You Care

ISO: What is it?

Exercise: Depth of Field

Depth of Field: Another View

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